Present techniques for assembling motor vehicles are tending towards making modules of varying degrees of complexity that are prepared off the assembly line, and that are subsequently fitted to the vehicle body together with all of the members with which they are fitted, thereby considerably shortening assembly lines and the time required to manufacture vehicles.
Thus, light units are conventionally mounted on receiver structures of the front end module type, being positioned and oriented on such receiver structures in compliance with dimensions that are defined relative to an ideal vehicle body. The ideal vehicle is represented by a gauge which serves as the frame of reference while the light units are being secured to the receiver structures.
In practice, vehicle bodies present relatively large dimensional variations, so modules fitted to such bodies can position light units in non-satisfactory manner. It can then be found necessary to perform subsequent adjustment in order to reposition the light units.
More precisely, the difficulty results from the fact that the tolerance ranges on a plurality of parts are cumulative at the time of mounting light units.
Apart from the tolerance ranges specific to a light unit and to the body, use of a gauge adds tolerance ranges associated firstly with the positioning of the light units on the module relative to the gauge, and secondly to the positioning of the module on the body.